In the related art, there are known laser microscope apparatuses that use PMTs (photomultiplier tubes) as detectors (for example, see Non Patent Literature 1). In addition to PMTs, other known types of detectors are PPDs (Pixelated Photon Detectors, multipixel photon detectors), such as MPPCs (Multi-Pixel Photon Counters), SiPMs (Silicon Photomultipliers), and multipixel avalanche photodiodes.
When detecting light, if a PPD is used in an operating mode in which a constant-intensity signal is output regardless of the intensity of the light, that is to say, a Geiger mode, it is possible to detect ultraweak light at the level of a single photon. In addition, in the case where a PPD is used in the Geiger mode, the number of photons that can be detected per unit time is on the order of 1 photon per pixel; however, since a PPD is a multipixel device, even if a large number of photons is incident on the PPD, it is possible to detect the number of photons corresponding thereto. In other words, a PPD can widen incident light-intensity range.